Robust Timing Synchronization Research Articles

A Robust Timing Synchronization Algorithm Based on PSSS for LTE-V2X

In recent years, Long-Term Evolution Vehicle-to-Everything (LTE-V2X) communication technology has received extensive attention. Timing synchronization is a crucial step in the receiving process, addressing Timing Offsets (TOs) resulting from random propagation delays, sampling frequency mismatches between the transmitter and receiver or a combination of both. However, the presence of high-speed relative movement between nodes and a low antenna height leads to a significant Doppler frequency offset, resulting in a low Signal-to-Noise Ratio (SNR) for received signals in LTE-V2X communication scenarios. This paper aims to investigate LTE-V2X technology with a specific focus on time synchronization. The research centers on the time synchronization method utilizing the Primary Sidelink Synchronization Signal (PSSS) and conducts a comprehensive analysis of existing algorithms, highlighting their respective advantages and disadvantages. On this basis, a robust timing synchronization algorithm for LTE-V2X communication scenarios is proposed. The algorithm comprises three key steps: coarse synchronization, frequency offset estimation and fine synchronization. Enhanced robustness is achieved through algorithm fusion, optimal decision threshold design and predefined frequency offset values. Furthermore, a hardware-in-the-loop simulation platform is established. The simulation results demonstrate a substantial performance improvement for the proposed algorithm compared to existing methods under adverse channel conditions characterized by high frequency offsets and low SNR.

Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel.

This paper proposes a robust symbol timing synchronization scheme for return link initial access based on the Digital Video Broadcasting-Return Channel via Satellite 2nd generation (DVB-RCS2) system for the Low Earth Orbit (LEO) satellite channel. In most cases, the feedforward estimator structure is considered for implementing Time Division Multiple Access (TDMA) packet demodulators such as the DVB-RCS2 system. More specifically, the Non-Data-Aided (NDA) approach, without using any kind of preamble, pilot, and postamble symbols, is applicable for fine symbol timing synchronization. However, it hinders the improvement in estimation accuracy, especially when dealing with short packet lengths during the initial access from the User Terminal (UT) to the Gateway (GW). Moreover, when a UT sends a short random access packet for initial access or resource request to the LEO satellite channel, the conventional schemes suffer from a large Doppler error depending on UT's location in a beam and satellite velocity. To ameliorate these problems, we propose a novel symbol timing synchronization algorithm for GW, and its advantage is confirmed through computer simulation.

Robust timing and frequency joint synchronization method for QNSC-enabled security optical communications system based on CO-OFDM

The security of optical fiber communication network has been paid more and more attention, and Quantum Noise Stream Cipher (QNSC) can guarantee its physical layer security. However, the QNSC system realized with CO-OFDM technology is very susceptible to timing synchronization error and carrier frequency offset. Existing symbol timing and frequency synchronization algorithms based on preambles have problems of timing metric platform, interference of side lobes, and low timing and frequency synchronization accuracy especially in optical signal transmission scenario of high-order modulation and low SNR. Furthermore, the preamble is not encrypted, which can be easily identified by illegal receiver. In order to solve above problems, a robust timing and frequency joint synchronization algorithm is proposed. The algorithm is composed of the preamble interleaved by conjugate, negative and image sequences of original element sequence. The preamble conforms to the preamble structure of Schmidl, Minn and CNI by adding negative and conjugate operator at the specific interval of the preamble. The correspond timing metric method, i.e. combination of Schmidl, Minn and CNI timing metric strategies, can fully extract characteristics of the preamble, and then timing and frequency joint synchronization is accurately obtained. For timing synchronization, experiments in 10Gbit/s CO-OFDM based QNSC system have illustrated that proposed algorithm has better timing synchronization performance than baseline algorithms. The detection probability is augmented and timing offset mean is decreased than that of baseline algorithms especially at low SNR. The simulation illustrates that proposed algorithm has more accurate frequency offset (FO) estimation performance compared with the baseline algorithms even at low SNR. Furthermore, the simulation illustrates the security performance of CO-OFDM based QNSC system is improved by encrypting the preamble with secret key.

Passive all-optical synchronization for polarization-maintaining mode-locked fiber lasers.

We have proposed and implemented for the first time to our knowledge a passive and all-optical pulse synchronization for polarization-maintaining fiber lasers. Specifically, the synchronization system was comprised of two independent Yb-doped and Er-doped mode-locked fiber lasers in a master-slave configuration. Master pulses were injected into the slave laser cavity consisting of a nonlinear amplifying loop mirror, which provided an effective fast intensity modulator due to the periodic introduction of nonreciprocal phase difference. As a result, robust and tight timing synchronization was achieved with a cavity mismatch tolerance of 800 µm and a relative timing jitter of 26 fs within 1-MHz bandwidth. In combination with the all-polarization-maintaining structure of fiber lasers, long-term stable operation was demonstrated over 12 hours without the need for temperature stabilization and vibration isolation. The implemented synchronous laser system could find immediate applications such as pump-probe microscopy, two-color spectroscopy and nonlinear frequency mixing.

Low-Complexity and Robust Symbol Timing Synchronization Scheme for MIMO DVB-T2 Systems

The digital video broadcasting-terrestrial-second generation (DVB-T2) system provides the so-called P1 symbol as preamble for the fast synchronization tasks. In this paper, a simple and robust timing synchronization scheme for a multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO–OFDM)-based DVB-T2 system is proposed to improve the initial time and frequency synchronization performance. In doing so, the proposed synchronization scheme utilizes a decimated correlation for the P1 symbol timing detection, thus producing a sharper peak timing detection metric. A new timing detection metric can help the proposed scheme to be robust against frequency-selective fading. It is found that the proposed synchronization scheme works well with a reduced computational complexity and outperforms the conventional estimation scheme.

Robust joint fine timing synchronization and channel estimation for MIMO systems

This paper proposes a joint timing synchronization and channel estimation scheme for multiple-input single-output or multiple-input multiple-output communication systems. All timing offsets and channel impulse responses (CIR) of different transmit–receive links are obtained based on a well-designed training sequence arrangement. The proposed approach consists of three stages at each receive antenna. First, a coarse timing offset (CTO) estimation algorithm is performed to estimate the CTO and the inter-transmitter delays. Then, relative timing indices and the corresponding CIR estimates of all transmit–receive links at the second stage are obtained using the generalized maximum-likelihood estimation based on a sliding observation vector. Finally, the fine time adjustment based on the minimum mean-squared error criterion is performed. From the simulation results, the proposed approach has excellent timing synchronization performance under several channel models at very low signal-to-noise ratio which is smaller than 1 dB. Also, the channel estimation performance in the proposed scheme approaches to the Cramér–Rao bound.

Robust Timing Synchronization for Multicarrier Systems Based on RST Invariance

In this paper, a blind robust timing synchronization method, based on invariance properties and cyclostationarity, for multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) is proposed and evaluated. Its results outperform the state-of-the-art for blind methods, specially in hard wireless channels where our proposal is highly superior. It even surpasses the performance of most of non-blind (pilot-aided) methods, while at the same time, it gets the advantages of energy and bandwidth saving of blind proposals. Moreover, since this technique does not require the use of pilots, it can be easily applied to either packet-based or broadcasting systems.

Robust Timing and Frequency Synchronization for OFDM Systems

This paper deals with timing and frequency synchronization in orthogonal frequency-division multiplexing (OFDM) systems. A robust multistage scheme that works in the time domain, independent of the preamble structure, is proposed. After coarse-timing estimation, joint timing and integer frequency synchronization is performed. Then, fractional frequency correction is carried out, and finally, fine-timing estimation completes the synchronization process. The new timing estimation method is flexible and can be adjusted according to the degree of channel distortion. Furthermore, frequency synchronization is efficiently accomplished with an estimation range that is as large as the bandwidth of the OFDM signal. The performance of the proposed method is evaluated in terms of the mean square error. The results indicate that the new method significantly improves performance compared with the previous methods.

Robust time-domain timing and frequency synchronization for OFDM systems

A robust and efficient technique for frame/symbol timing and carrier frequency synchronization in OFDM systems is presented. It uses a preamble consisting of only one training symbol with two identical parts to achieve reliable timing and frequency accuracy in the time-domain, over a wide frequency estimation range which can be up to half of the signal sampling frequency. Also, it has a low complexity which is adaptive to the degree of channel distortion. Computer simulations in the Rayleigh fading ISI channel show that the proposed method achieves superior performance to existing techniques in terms of timing and frequency accuracy. Also, its operation in the time-domain helps to achieve faster synchronization convergence.

Robust and Accurate Frequency and Timing Synchronization Using Chirp Signals

We propose a new robust and accurate synchronization procedure using a training sequence composed of chirp signals. We use a new integer frequency estimation algorithm and propose a new combination of a known fractional frequency offset estimation algorithm and timing synchronization algorithm. The training sequence is composed of one up and two down chirp symbols, also known as Newman phases. The integer frequency offset estimation algorithm uses the effect of timing and frequency offsets on the matched filter outputs of the chirp signals. Autocorrelation and reversed autocorrelation are used to acquire the timing instant and the fractional frequency offset. We present the complete timing and frequency synchronization procedure and study the output signals of the autocorrelation and reversed autocorrelation algorithms. Finally, we check the performance of the synchronization procedure via Monte Carlo simulation in several multipath channels. Our algorithms are accurate and more robust compared to previously published state-of-the art algorithms.

Robust and Low-Complexity Timing Synchronization Algorithm and its Architecture for ADSRC Applications

5.9 GHz advanced dedicated short range communications (ADSRC) is a short-to-medium range communication standard that supports both public safety and private operations in roadside-to-veh ...

A robust timing synchronization design in OFDM systems-part I: low-mobility cases

In this paper we consider the design of a robust timing synchronization algorithm for pilot-aided OFDM systems in high-mobility fading environments. We first analyze the impact of both mobility and timing errors on the performance of a pilot-aided OFDM system for frequency selective fading channels, by deriving an expression for channel estimation error variance. The analysis will show that, even for high levels of mobility, a pilot-aided channel estimator is considerably sensitive to timing errors, due to the impact of rotations in different bases. We then show how this sensitivity can be utilized to design a robust timing synchronization algorithm for mobile OFDM systems, without relying on synchronization training information. Theoretical results are then confirmed by simulating the performance of an OFDM system in high delay and Doppler spread fading environments. Finally, we show how the proposed mathematical framework and algorithm can be used to address timing synchronization in the presence of a frequency offset as well. The analysis of this paper is the extension of the derivations of Part I [8], the accompanying paper on the design of a robust timing synchronizer for low-mobility OFDM systems.

Robust timing synchronization design in OFDM systems - Part II: high-mobility cases

In this paper we consider the design of a robust timing synchronization algorithm for pilot-aided OFDM systems in high-mobility fading environments. We first analyze the impact of both mobility and timing errors on the performance of a pilot-aided OFDM system for frequency selective fading channels, by deriving an expression for channel estimation error variance. The analysis will show that, even for high levels of mobility, a pilot-aided channel estimator is considerably sensitive to timing errors, due to the impact of rotations in different bases. We then show how this sensitivity can be utilized to design a robust timing synchronization algorithm for mobile OFDM systems, without relying on synchronization training information. Theoretical results are then confirmed by simulating the performance of an OFDM system in high delay and Doppler spread fading environments. Finally, we show how the proposed mathematical framework and algorithm can be used to address timing synchronization in the presence of a frequency offset as well. The analysis of this paper is the extension of the derivations of Part I [8], the accompanying paper on the design of a robust timing synchronizer for low-mobility OFDM systems.

Robust Timing and Frequency Synchronization Scheme for DTMB System

In this paper a robust timing and frequency synchronization algorithm for DTMB system is developed. A two-step frequency offset estimation and compensation process is proposed to perform carrier recovery. Firstly coarse frequency estimation is achieved by utilizing the shift-and-add property of m-sequence. The second step finds the frame start position and the remaining frequency offset simultaneously. Meanwhile a timing tracking strategy is proposed to effectively track the dynamic changes in mobile environment. Thus the proposed scheme can resist large frequency offset and achieve accurate timing and frequency estimation. Simulation results under different channel situations verify the performance of the proposed scheme.

Analysis of the Narrowband Interference Effect on OFDM Timing Synchronization

In OFDM systems, the symbol timing synchronization is needed to find an estimate of where the symbol starts. The most popular of the pilot-aided timing estimators is the one proposed by Schmidl and Cox (S&C) ["Robust Frequency and Timing Synchronization for OFDM," <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IEEE Transactions on Communications</i> , vol. 45, no. 12, pp. 1613-1621, Dec. 1997]. Generally, the proper action of the timing estimator may be strongly affected by the presence of disturbances, like narrowband interference (NBI) signals. This paper investigates the effect of NBI signals, which may arise in the OFDM band as the spectrum becomes more crowded, on the timing synchronization for OFDM systems. The performance of the S&C symbol timing synchronizer is evaluated in an analytical way in the presence of narrowband interferers. Also, the probabilities of both missing and false detection of a training sequence are addressed. Further, simulations have been carried out to verify the validity of the approximations in the analysis.

A Robust Timing Synchronization Algorithm for OFDM Systems over Multipath Rayleigh Fading Channels

In this paper, we propose a robust timing synchronization algorithm for wireless MAN OFDM systems. The proposed algorithm is composed of frame synchronization and FFT timing synchronization. The conventional correlation scheme for estimation of timing offset has an ambiguity in the detection of accurate symbol timing. The proposed scheme, however, shows a clear peak at the correct timing by using the conjugate-symmetric characteristic of preamble and is able to control the FFT window position continuously with the 1-st order loop filter. Simulation results demonstrate the superiority of the proposed algorithm.

A Robust Timing and Frequency Synchronization Algorithm for DVB-H Receiver

A robust symbol timing and carrier frequency synchronization scheme applicable to orthogonal frequency division multiplexing system is presented. The proposed method is based on correlation and energy detection in time domain. The estimator has a steep timing metric and can provide delay-spread information about the channel. It means that the proposed method can distinguish ISI (inter-symbol interference) free region from ISI region with optimum timing position acquired. The computer simulation results show that the proposed algorithm can track time varying channel condition and has much smaller MSE (mean squares error) than that of ML estimation algorithms.

A robust timing and frequency synchronization for OFDM systems

A robust symbol-timing and carrier-frequency synchronization scheme applicable to orthogonal frequency-division-multiplexing systems is presented. The proposed method is based on a training symbol specifically designed to have a steep rolloff timing metric. The proposed timing metric also provides a robust sync detection capability. Both time domain training and frequency domain (FD) training are investigated. For FD training, maintaining a low peak-to-average power ratio of the training symbol was taken into consideration. The channel estimation scheme based on the designed training symbol was also incorporated in the system in order to give both fine-timing and frequency-offset estimates. For fine frequency estimation, two approaches are presented. The first one is based on the suppression of the interference introduced in the frequency estimation process by the training symbol pattern in the context of multipath dispersive channels. The second one is based on the maximum likelihood principle and does not suffer from any interference. A new performance measure is introduced for timing estimation, which is based on the plot of signal to timing-error-induced average interference power ratio against the timing estimate shift. A simple approach for finding the optimal setting of the timing estimator is presented. Finally, the sync detection, timing estimation, frequency estimation, and bit-error-rate performance of the proposed method are presented in a multipath Rayleigh fading channel.

A robust timing synchronization scheme in multiple antenna systems with Doppler frequency shifts

We propose a timing synchronization scheme for a dual antenna system in Rayleigh-fading environments. Instead of assuming the channel gain to be constant during the training duration, we consider the time-variant nature of the multiplicative distortions and formulate them with linear combinations of eigenfunctions. Then, we derive a formula to find the maximum-likelihood estimation of the channel timing and simulate the performance with both ideal and nonideal channel state information. The results show that this approach outperforms the conventional ones especially when the Doppler spread is severe.

Robust frequency and timing synchronization for OFDM

A rapid synchronization method is presented for an orthogonal frequency-division multiplexing (OFDM) system using either a continuous transmission or a burst operation over a frequency-selective channel. The presence of a signal can be detected upon the receipt of just one training sequence of two symbols. The start of the frame and the beginning of the symbol can be found, and carrier frequency offsets of many subchannels spacings can be corrected. The algorithms operate near the Cramer-Rao lower bound for the variance of the frequency offset estimate, and the inherent averaging over many subcarriers allows acquisition at very low signal-to-noise ratios (SNRs).